This invention relates to components of absorbent products and absorbent products. More specifically, this invention relates to fibers and structures of the fibers that acquire, distribute and store fluids for use in absorbent products.
Cellulose fluff pulp is a common component in the core of disposable absorbent products, such as diapers, catamenials, and incontinent pads. Cellulose fluff pulp is relatively inexpensive. Superabsorbent polymer (SAP) in fiber or powder form is another component that is often found in the core of disposable absorbent products. Core materials like cellulose fluff pulp, chemically modified fluff pulp, or SAP are not easily desorbed because the thermodynamic attraction of aqueous liquids for these materials is extremely high. Hence, liquid in a region containing these materials generally cannot be transported through or away from that region making fluid distribution difficult. Cellulose fluff pulp also collapses when saturated with liquid. This collapse has long been a problem in the absorbent products art limiting their utility.
U.S. Pat. Nos. 4,898,642 to Moore et al.; 4,888,093 to Dean et al.; 4,889,596 to Schoggen et al. and 4,976,819 to Minton describe various chemically modified fluff pulps directed to remedy the deficiencies of untreated fluff pulp.
U.S. Pat. No. 3,219,739 to Breen discloses poly(ethylene terephthalate) (PET) fibers and a process for making those fibers. The fibers disclosed in the ""739 patent are characterized by having arms, a relatively high spatial frequency, and relatively short-range sinuous (ruffle) or spiral geometries in the arms. The relatively short range is on the order of ten microns. The fibers disclosed in the ""739 patent will not spontaneously transport water. That is, a liquid in contact with the cross-section of a single one of the fibers disclosed in the ""739 patent will not continuously spread from the place of contact along the length of the fiber.
U.S. Pat. No 5,611,981 to Phillips et al. discloses spontaneously wettable fibers having a combination of X values and surface contact angles that satisfy conditions for spontaneous wetting. The X factor is defined therein as X=Pw/(4r+(xcfx80-2)D) where Pw is the wetted perimeter of the filament, r is the radius of the circumscribed circle circumscribing the fiber""s cross-section, and D is the minor axis dimension across the fiber""s cross-section. The teachings of the ""981 patent are hereby incorporated herein by reference as if fully set forth herein.
U.S. Pat. No. 5,200,248 to Thompson et al. discloses capillary channel polymeric fibers, which store and transport liquid. The fibers have non-round cross-section shapes which include relatively long thin portions. The cross-section shapes are the same along the length of the fiber. The ""248 patent discloses that these capillary channel fibers may be coated with materials that provide an adhesion tension with water of at least 25 dynes/cm. The teachings and especially the definitions in the ""248 patent are hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 5,268,229 to Phillips et al. discloses fibers having non-round cross-sectional shapes, specifically xe2x80x9cUxe2x80x9d and xe2x80x9cExe2x80x9d shaped cross-sections with stabilizing legs. These fibers are also spontaneously wettable fibers and have cross-sections that are the same along the length of the fiber.
Co-pending U.S. application titled xe2x80x9cBundles of Fibers Useful for Moving Liquids at High Fluxes and Acquisition/Distribution Structures that Use the Bundlesxe2x80x9d filed Aug. 15, 1997, discloses bundles of fibers for use as distribution materials. The individual fibers themselves are poor distribution materials having no intra-fiber capillary channels. When combined with each other in bundles, the bundles become excellent distribution materials by utilizing inter-fiber capillary channels. The teachings of and especially the definitions are hereby incorporated herein by reference as if fully set forth herein.
A highly distorted, bulky synthetic polymeric fiber acquires, distributes and stores fluids when made into an absorbent structure having a large number of the fibers in close proximity to one another. The fibers have a length of between 2 and about 37 millimeters, cross-sections that vary in shape along the length of the fiber, a single fiber bulk factor between 0.5 and 10.0, a short range distortion factor greater than 5, and a long range distortion factor between 0.05 and 0.9. In several preferred embodiments the fiber has at least one cross-section along its length that is characterized as having a distorted xe2x80x9cHxe2x80x9d shape, a distorted xe2x80x9cYxe2x80x9d shape, a distorted xe2x80x9c+xe2x80x9d shape, a distorted xe2x80x9cUxe2x80x9d shape, or a distorted shape of a fiber having a cross-section as shown in FIG. 17. The fibers are primarily for use in absorbent products such as diapers, catamenials, and incontinent devices, thus the fibers preferably have an adhesion tension on their surface of greater than 25 dynes/cm with distilled water for adequate movement of aqueous fluids. The fiber surface may be coated with a superabsorbent polymer or a blend of superabsorbent polymer and surfactant.
The absorbent structure comprising the novel fibers of the invention function to manage fluids by temporarily acquiring and distributing fluids. When the novel fibers are coated with a superabsorbent polymer or combined with other materials such as fluff pulp, chemically modified fluff pulp, superabsorbent polymer or combinations thereof, the absorbent structure created functions to permanently store fluids. These absorbent structures have improved water absorbency, decreased wet collapse and reduce water release over many conventional absorbent structures. The absorbent structures in combination with top sheets, distribution layers, shielding layers, storage cores, and back sheets make excellent absorbent products with reduced leakage, improved absorbency and complete utilization of the storage core.
Processes for making the novel fibers of the invention include the step sequences of (1) spinning, optionally drawing, cutting, and shrinking or (2) spinning, optionally drawing, shrinking, and cutting. These processes may be done continuously and at high speeds.